You can be forgiven if you’ve forgotten about the HBO crime anthology series.

The first season, in 2014, was a sensation, starring Matthew McConaughey and Woody Harrelson as Louisiana homicide detectives tracking a bizarre serial killer for almost 20 years. The eight episodes from creator Nic Pizzolatto stand as one of the finest accomplishments in television, with a story that measured the price of the pursuit of justice to one’s very soul.

The second season, in 2015, was a disaster, despite Colin Farrell’s fine performance as a surly California detective drawn into a conspiracy involving crooked cops and a Mexican drug cartel.

Four years later — or approximately 2,000 TV series premieres later — Pizzolatto returns with another installment, this one starring newly minted Golden Globe winner Mahershala Ali (“Green Book”). McConaughey and Harrelson are credited as executive producers.

The good news: This season is more season one “True Detective” than season two “True Detective,” with Ali giving a tour de force performance as the show toggles between three time periods.

The bad news? The central mystery is more fitting for a CBS crime procedural, and over eight episodes is stretched to its limit. (HBO provided the first five episodes for review. Minor spoilers follow.)

In 1980 Ozarks, two children, brother and sister, set out on their bikes to visit a pal and his new puppy.

They never return.

The investigation into what happened to them roils their small, impoverished town, leads to an exorbitant body count and hijacks Detective Wayne Hays’ (Ali) personal and professional lives.

In 1990, Hays and his onetime partner Roland West (Stephen Dorff, “Star”) are forced to reunite to reopen the case after a new piece of evidence challenges everything they believed.

In 2015, Hays suffers from dementia and is racing against time to understand a crime and its repercussions before his mind is obliterated.

Ali’s performance as old man crumbling as the loss of his vast intelligence accelerates is wrenching. The old-age makeup is the best this viewer has ever seen and is utterly convincing. If there is any justice, come Emmy time he will get a little buddy to keep his Golden Globe company.

In the supporting cast, Scoot McNairy (“Halt and Catch Fire”) and Mamie Gummer (“The Good Wife”) as the children’s parents, at war with each other, are electrifying. Carmen Ejogo (“Selma”) as Amelia, a teacher who becomes Hays’ touchstone, is solid in a role that doesn’t have much weight.

There’s a revelation at the climax of the first half of the two-hour premiere that changes everything about the investigation, yet the show doubles back to scenes that are ultimately pointless. Bits of the crime scene — especially straw dolls — echo elements of the first season but are played to lesser effect. We are reminded countless times that Hays is a tracker, that he served in Vietnam.